Essential elements of such a ground milling machine are a machine frame supported by travelling devices, a drive engine providing the drive energy required for travelling and working operation, as well as a milling device. The milling device particularly is a milling drum, comprising a support tube equipped with a plurality of chisel devices on its outside jacket surface. The milling drum is usually arranged transversely to the working direction and horizontally with its rotation axis and mills the ground during working operation. Typical areas of application of generic ground milling machines are, for example, cold milling of bitumen surfaces, stabilizing and/or recycling of the ground or extraction of ground natural resources by means of so-called surface miners.
During working operation of such a ground milling machine, the treatment of the milled material, for example, the removal of the milled material from the region of the milling drum, is of particular importance. In order to achieve a controllable flow of the milled material, the milling drum is typically arranged in a milling drum box comprising side walls, a front wall (i.e., in the working direction in front of the milling drum) and a rear wall (in the working direction behind the milling drum) as well as a termination upward. This results in a defined inner space in which the milling drum rotates during working operation and in which the milled material is routed. Usually the milled material is either laid on the ground or supplied to a suitable transport device, for example, a conveyor belt, and thereby removed from the milling spot. In order to achieve a most clean milling bed, which is particularly desired in the case of maintenance work on road surfaces but also when extracting natural resources with a generic ground milling machine, for example, the rear wall arranged behind the milling drum in the working direction is often times at least partially configured as a so-called stripping device. Said stripping device is carried along having a bottom edge extending transversely to the milling bed and resting on said bed and strips off loose material located on the milling bed. Additionally or alternatively, a grading of the milling bed and/or the regulation of the material volume remaining on the milling bed can be achieved by means of such a stripping device, for example. Such a generic stripping device is known from DE 10 2007 038 677 B4, DE 35 280 038 C2 and DE 10 2012 012 607 A1, for example, to which reference is made hereby with respect to the application of the generic stripping device.
An essential element of the stripping device is a stripping plate, often times having an upper plate and a bottom plate. In this case, the stripping plate thus comprises two plate-type elements, the bottom plate being guided on the upper plate in a height-adjustable manner and is adjustable in its position relative to the upper plate in the vertical direction between an upper “top position” and a lowered “extension position”. As a result, the bottom plate may, for example, be lowered so far (and partly even be actively pressed onto the ground of the milling bed) that it scratches over the surface of the milling bed with its bottom edge, thus forming a rearward termination which is almost tight for the milling material. As an alternative, the bottom plate may be lifted so that milled material partially or completely remains on the milling bed.
The working devices of the milling drum, for example, round shaft chisels, are subject to heavy wear due to the comparatively great material stress and thus need to be replaced regularly during working operation. This requires access to the milling drum. Further devices are also often times arranged inside the milling drum box, such as injection devices for water and/or foamed bitumen, etc., which need to be accessible for maintenance purposes. For this reason, in the region of the upper plate, and, in particular, in the region of the upper end of the upper plate, the stripping plate is often times mounted such that it can pivot about a horizontal pivot axis between a pivot-up position and a pivot-down position. The pivot-up position defines the position in which the stripping plate is pivoted upward, or folded upward, about the pivot axis. In said position, the upper plate and the bottom plate are together in the pivot-up position, so that the milling drum can be accessed from the outside, for example, for maintenance purposes. From the pivot-up position, the stripping plate may be pivoted into a pivot-down position, in which case the upper plate is pivoted downward about the pivot axis together with the bottom plate until at least the upper plate produces a spatial termination to the rear and rests in or against the side walls of the milling drum box, for example. Depending on the set height adjustment of the bottom plate on the upper plate, there will be a free space, or no free space, between the bottom edge of the bottom plate and the milling bed.
The drive of the adjustment of the stripping plate is effected via actuators, which may particularly be a pair of hydraulic cylinders. Said actuators are usually arranged non-centrally, i.e., spaced apart from one another and offset towards the edges of the milling drum box. For driving the pivot movement of the stripping plate and/or the height adjustment of the stripping plate, particularly the bottom plate on the upper plate, in each case separate actuators, as, for example, described in DE 10 2007 038 677 B4, may be used, or actuators may be used in a combined manner, as, for example, indicated in DE 10 2012 012 607 A1. It is known for hydraulic cylinders to provide manually adjustable restrictors, by means of which a reasonably synchronous operation of the actuators may be realized. However, said process is very time-consuming and needs to be repeated regularly due to the fact that friction values between the milling drum box and the stripping plate may change very rapidly during operation, for example.
It is very important for the proper handling of the adjustable stripping plate that the pivoting-up and pivoting-down of the stripping plate and/or the height adjustment of the stripping plate or at least of the bottom plate can be performed in a trouble-free and reliable manner. However, this requires a robust parallel adjustment of the at least two actuators, since otherwise the stripping plate may get jammed or blocked on the milling drum box and may impair its functionality. At the same time, such jamming or blocking increases wear to guiding elements for the stripping plate, which results in undesired reduction of its service life.